Answer:
The CaCl2 solution is 1.0M. The closest option is d) 0.96 M. Perhaps the value of Avogadro's number has changed slightly from the value of 6.022 x 10^23 used here.
Step-by-step explanation:
It is useful to remember the definition of Molar (M). It is concentration expressed as moles/liter. 1 mole of NaCl dissolved in 1 liter of water provides a 1 M solution. 1 mole of NaCl in 500ml (0.5 liters) would make a 2 M solution (1 mole/0.5L) = 2M
In this problem, we are told 3.011 x 10^23 chloride ions are present when CaCl2 is dissolved. Avogadro's number says 6.02 x 10^23 ions (or molecules) are equal to 1 mole. We have:
(3.011 x 10^23 chloride ions)/(6.02 x 10^23 chloride ions/mole) or
0.50 mole Cl ions
Since CaCl2 releases 2 Cl ions per molecule of CaCl2, we must have started with 0.25 [0.50/2] moles of CaCl2.
We were told that the CaCl2 was dissolved in 250 ml of solution. Convert to liters: 0.250 liters.
0.25 moles in 0.250 liters means that the molarity of the solution is (0.25 moles CaCl2)/(0.25 L) = 1.0 mole/liter or 1.0 mole